Sentinel-3 and the ocean carbon conundrum

An international team of researchers, including PML scientists, is using pioneering techniques to study how carbon dioxide is transferred from the atmosphere into the oceans.

Each year, about a quarter of the carbon dioxide we release into the atmosphere ends up in the ocean, but how it happens is still not fully understood. The Sentinel-3A satellite is poised to play an important role in shedding new light on this exchange.

As more carbon dioxide dissolves into the oceans, it leads to ocean acidification, making it difficult for some marine life to survive. Monitoring and understanding the carbon cycle is important because carbon is the fundamental building block of all living organisms. Also, the process of carbon moving between the oceans, atmosphere, land and ecosystems helps to control our climate.

Over the last four years an international team of researchers and engineers including PML scientists has been using satellites along with measurements from ships and pioneering cloud computing techniques to study how carbon dioxide is transferred from the atmosphere into the oceans.

Their new work, published in the Journal of Atmospheric and Oceanic Technology, reveals that the seas around Europe absorb an astonishing 24 million tonnes of carbon each year. This is equivalent in weight to two million double decker buses or 72 000 Boeing 747s.

The team is making their data and cloud computing tools, the ‘FluxEngine’, available to the international scientific community so that other groups can analyse the data for themselves.

PML scientists were responsible for writing the software at the heart of the Flux Engine that calculates the air-sea CO2 fluxes, and continues with its development, recently focusing on developing new ways to estimate oceanic CO2 for use in the Flux Engine, along with estimates of its uncertainty.

Peter Land, PML Co-Investigator on the project, commented: “For climate research, it is crucial that we use consistent and quality-controlled data, processed in a reproducible and transparent way. The freely available Flux Engine software and data is a significant step towards this”.

The team hopes that making tools like this available to everyone will improve the transparency and traceability of climate studies. It should also help to accelerate scientific advancement in this important area.

They are also now looking to Europe’s Copernicus Sentinel satellites to provide vital information for this area of research. Sentinel-3A was launched on 16 February and once commissioned for service it will measure the temperature of the sea surface, currents, winds, waves and other biochemical factors.

The unique aspect of Sentinel-3A is that its instruments make simultaneous measurements, providing overlapping data products that carry vital information to estimate carbon dioxide ‘fluxes’. To calculate the flux of gases between the ocean and the atmosphere, it is necessary to know the solubility of carbon dioxide in the seawater, together with the speed of gas transfer. Importantly, the solubility is determined by a combination of sea-surface temperature and salinity, while the ocean surface wind and wave environment govern the speed at which carbon dioxide is transferred.

All this information from just one satellite makes the Sentinel-3 mission a near-perfect tool to estimate the exchange of carbon dioxide between the atmosphere and the global ocean, as well as seasonal, year-to-year and regional patterns in the exchange.

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